Note: Descriptions are shown in the official language in which they were submitted.
1~48516
L~UBRICATING ODL CO~POSlTlON5 CO~rrAUN~NG NOV a
CO~BlNA n ON CXF ST~U3nLlZERS
The present invention relates to novel lubricating oil compositions,
5 and particularly to lubricating oil compositions containing a novel
stabilizer/antioxidant system comprising high molecular weight phosphites and
hindered phenols.
In most applications of lubricating oils which are to be used at
elevated temperatures, it is desirable that the lubricating oil formulation
lû exhibit good oxidation resistance, in order to minimize or prevent the
formation of sludge increase in viscosity and acidity of the lubricant, and the
consequent lowering of the lubricating ability of the oil and lubricating system
in general.
In the prior art, many materials have been disclosed to improve
high-temperature oxygen stability and resistance to discoloration, including
calcium naphtha sulphonates, barium versatates, calcium phenates, and various
phenols, phosphates and phosphites. However, conventional stabilizing systems
have shown limited success when used with certain primarily paraffinic
lubricating oils, and hence there is a need for a reliable stabilizing system for
20 use with these oils.
Phosphites are known in the art as stabilizers for lubricating oils.
In U.S. Patent 3652411, Commichau disclosed a mixture of phosphite, phenol,
substituted amine, organic phosphate, polyhydroxyquinone and benzotriazole as
a stabilizer for polyglycol lubricant. There was no discussion of
25 subcombinations of this rather complex mixture. Orloff et al. in U.S. Patent
3115463 disclosed the stabilization of mineral oils and synthetic diester oils by
a synergistic mixture of dialky; hydrogen phosphite and substituted phenol or
. ~.
~8516
bisphenol. U.S. Patent 3115464 by the same inventors disclosed an orthoalkyl
phenol in admixture with dialkyl hydrogen phosphite, where ths alkyl groups
were isopropyl or tertiary butyl. Spivack et al. in U.S. Patent 4374219
disclosed a phosphite stabilizer which was an alkanolamine ester of a non-
cyclic and a cyclic phosphite. It was said to be useful as a stabilizer for
lubricating oils and polymers, alone or in combination with selected hindered
phenols, including some of the hindered phenols of the present invention.
However, hydrotreated oils present particular problems for stabilizers in hot
oxygen or air exposure of lubricating oils, as ackno~ledged in Canadian Patent
1185962 of Bijwaard et al. That patent disclosed a hydrotreated oil having
poor oxidation stability to which was added a substantial quantity of less
severely hydrotreated oil containing some remaining sulphur. Nevertheless,
there remains a need for a really effective stabilizer for use with hydrotreatedoils, poly-alpha-olefins and paraffinic white oils.
Accordingly, the invention provides a lubricating composition
comprising a major amount of lubricating oil selected from the group
consisting of hydrotreated oil, poly-alpha-olefin oil and paraffinic white oil,
and an antioxidant amount of a synergistic mixture of:
(a) a low-volatility organically substituted phosphite or diphosphite,
wherein the substituent groups are alkyl, aryl or alkylaryl, and said
phosphite contains substantially no hydroxy groups, and
(b) a low-volatility sterically hindered phenolic compound.
Lubricating compositions according to the invention exhibit superior oxidation
resistance as measured by, for exarnple, an IP-48 test carried out for 24 hours
at 200C. In this test, the sample is subjected to relatively severe oxidation
conditions by heating to 200C and passing air through it at 15 litres per hour.For the purposes of the present disclosure the oxidation was carried out for
. . .
~2'18516
four six-hour periods instead of the normal two periods, such that the sample
was subjected to oxidation for 24 hours in total. The change in viscosity and in
Total Acid Number of the sample are the properties of primary interest and
are reported herein. At the same time, the compositions according to the
5 invention exhibit no significant discoloration after 24 hours in the modified IP-
48 test. It is also advantageous in many applications that the lubricants of the
invention exhibit high clarity throughout their operating life for several
reasons, including the reason that a clear lubricant can be seen by eye not to
contain significant amounts of suspended solids; because suspended solids can
10 be abrasive in use, it is useful that their absence can be detected visually.
The hindered phenol of the invention comprises compounds having
alkyl groups at the ortho positions on the ring with respect to the hydroxyl
group. The presence of these inhibiting alkyl groups slows the sacrificial
oxidation of the phenol to increase its effectiveness as an antioxidant in the
15 lubricating oil. The phenol compounds are preferably selected from
compounds having the formula
(i) ~ Rl O
H(~// ~ C C Cl----O --C~ ¦ --C~
wherein R1 and R2 are selected from the group isopropyl and tertiary butyl,
and n is 2, 3 or 4, and compounds having the formula
-- 3 --
lZ4~35~3
(ii) ~ 2I 0
3~ 2_C 2 1l C 2--C~{2 --S
5 where Rl and R2 are independently isopropyl or tertiary butyl. For good
performance at high temperatures of the lubricating compositions of this
invention, it is critical that the volatility of the stabilizing antioxidants be low
at elevated temperatures. In this specification, low volatility denotes a
material that in a thermogravimetric analysis, loses no more than 5 per c~nt
10 of Its mass below laOC, when heated in air at a rate of 10
to 20 C/min, and further
that the rate of weight 108s is low up to 250C so that preferably the 50 per
cent losa temperature is above 300C. This characteristic is especially
suitable in lubricating compositions for use in heat transfer oils and
15 compressor oils which are generally subjected to high temperatures (180C -
300C) service. Such low volatility i3 required of both the phenol and the
phosphite antioxidanta in ths synergistic combination of the invention.
Preferred phenolic antioxidants in the invention are: Tetrakis (methylene -
3,5-ditert-butyl 4 hydroxy-hydrocinnamate) methane or thio-diethylene bis-
20 (3,5-di-tert-butyl-4-hydroxy-hydrocinnamate) methane.
The phosphite in the compositiona of the invention is preferably
selected from aromatic phosphites of the following formulae:
25 (i) ~ 2
where Rl and R2 are, independently, alkyl groups having from three to six
carbon atoms, and
-- 4 --
lZ4851
(ii~ r Rl
R2 {~ / CH2 ` C
L o - CH2 ~ ; 2
5 where R1 and R2 are, independently, alkyl groups having from three to six
carbon atoms. The phosphites in the compositions of the invention must be
hydrolytically stable, as measured by the ASTM D2619 test. In this test the
lubricating oil final composition including the stabilizing mixture is maintained
in contact with water at 93C in the presence of a copper coupon for 48 hours.
10 The weight loss of the coupon is measured, together with the acidity of the
water layer and other properties. The test measures the propensity of the
additives to be hydrolysed in the presence of water, heat and active metals. In
this test, a hydrolytically stable lubricating oil composition should produce an
increase in acidity in the water layer of no more than 1 mg KOH and Total
15 Acid l~umber change in the oil layer of no more than 0.1; and the weight loss
of the copper coupon should not exceed 0.1 mg/cm2. The successful
phosphites that are within the scope of the invention are tri-substituted, that
is, having all three of the hydrogen atoms replaced by organic substituent
groups. Preferred phosphites in the compositions of the invention are: tris-
20 (2,4-di-tert-butylphenyl) phosphite; and bis-(2,4-di-tert-butylphenyl
pentaerythritol) diphosphite.
The stabilizers of the invention are used in antioxidant amounts in
the lubricating compositions. Generally the total weight of stabilizers is from
0.05 per cent to 2 per cent, and preferably from 0.1 per cent to 1 per cent, of
25 the lubricating oil. The mixture of phenol and phosphite has been found to
have synergistic effect throughout the range of mixture ratios. The weight
ratio of phenol:phosphite is preferably from 1:6 to 1:2 where the phosphite
O .
. . .
~Z~851~
stabilizer comprises a phosphite of formula (i) having one phosphorus atom per
molecule, and from 1:5 to 1:1 where the phosphite stabilizer is of formula (ii)
having two phosphorus atoms per molecule.
The compositions of the invention are made from lubricating oil
5 selected from the group consisting of poly-alpha-olefin oils, paraffinic white
oils and in particular, hydrotreated oils. The latter oils are made from vacuum
gas oil fractions which have been subjected to a two-stage high-hydrogen-
pressure hydrotreating process in the presence of active zeolite catalysts.
Aspects of such process are disclosed in United States ~atent Numbers
10 3493493, 3562149,3761388, 3763033, 3764518, 3B03027, 39416B0 and 4285804.
In the first stage of a typical hydrotreatment process, the hydrogen pressure is
in the vicinity of 20 MPa and the temperature is maintained at about 390C,
using a fluorided Ni-W catalyst on a silica-alumina support; nitrogen-, sulphur-
and oxygen-containing compounds are almost entirely removed from the
15 feedstock; and other effects include a high degree of saturation of aromatics
and a high degree of ring scission of the polycyclic intermediates. Lubricating
oil fractions from the first stage are dewaxed and subjected to further
hydrogen treatment in the presence of a catalyst, for example, Ni-W on a
silica-alumina support, at lower temperature than the first stage. Aromatics
20 and olefins are further saturated in this stage. The product oil contains
substantially no sulphur or nitrogen, and only trace amounts of aromatics,
being substantially entirely composed of saturates including paraffins and
cycloparaff ins.
Examples of typical oils are shown in Table 1. Hydrotreated oils
25 are available from several manufacturers, two of which are included in the
Table as representative of the type. The near total absence of aromatics,
unsaturates, sulphur and nitrogen characterizes the hydrotreated oils.
~Z~516
.
o ~1~ o o 0 ~ -' ~ ~ '1~ ~------ "`I ~1
U~
-
o
. to O ~ o ~ ~ O ~
Z Z zl zl v~
I ~3
s
~1 ` ~ o olo z z z z -I -I '`' ~'
æ I ~
., b
~ a~
0 ~ Q~
S ~ U o = = U ~ ~, Z ~ ~ ~ E E
-- 7 --
. ~
851~
Poly-alpha-olefin oils are manufactured by
oligomerizing ole~ins, for example n-decene, which
are then saturated to remove the remainins
double bond. I hese materials by their naturE contain no sulphur, nitrogen,
S oxygen or aromatics.
Paraffinic white oils are made from canventional napthenic or
solvent-refined lubricating oils by contact with concentrated sulphuric acid to
remove aromatics, sulphur and nitrogen compounds. In recent years the acid
treatment has been supplemented by first subjecting the feedstocks to a mild
10 hydrogen treatment. All three types of lubricating oils are similar in that they
contain substantially no aromatics or unsaturated compounds and substantially
no heteroatoms. It is not clear whether the synergistic effect of the hindered
phenol and phosphite antioxidants of the invention occur because of the
substantially saturated nature of the lubricating oils to be protected, or
15 because of the absence of heteroatoms. What is known, as will be illustrated
hereinafter, is that the same combinations of antioxidants in naphthenic and
solvent-refined lubricating oils are not synergistic in their protection against
oxidation.
In addition, the lubricating compositions of the invention can
20 include other additives as necessary for the specific application in which the
lubricating oils are to be used, for example, rust inhibitors, defoamers,
demulsifiers, extreme pressure additives, viscosity index improvers and pour
polnt depressants. All of these materials are well known in the art of
formulating lubricating oils, and the person skilled in the art will be aware of
2 5 the need to select thermally stable additives suitable to the end-use
application of the particular lubrication product.
By way of example, typical lubricant products including lubricating
compositions according to the invention include the following. All amounts of
B
12~8~
ingredients are shown as percentages by weight and the remainder is
hydrotreated, paraffinic white, or poly-alpha-olefin lubricating oil to make up
100 per cent of the formulation.
5 1. Hydraulic Oil
Tetrakis-(methylene-3,5 di-tert-butyl-
4-hydroxy-hydrocinnamate) methane 0.2%
Tris-(2,4-di-tert-butylphenyl) phosphite 0.04%
Rust inhibitor 0.1/~
Vemulsifier 25 ppm
Defoamer 200 ppm
Pour point depressant 0.2%
Copper corrosion inhibitor 0.03%
2. Steam Turbine Oil
Tetrakis-(methylene-3,5 di-tert-butyl-
4-hydroxy-hydrocinnamate) methane 0.2%
Tris- ( 2, 4-di-tert-butylphenyl) phosphite 0.2%
Rust inhibitor-alkylsuccinate 0.1%
Demulsifier 25 ppm
Defoamer 200 ppm
Pour point depressant 0. 2%
Copper corrosion inhibitor 0.0~%
3. Compreæor Oil
Thio-diethylene bis-(3,5-di-tert-butyl-
4 hydroxy hydrocinnamte) 0.2%
Tris-( 2, 4-di-tert-butylphenyl) phosphite 0.2%
Rust inhibitor-alkylsuccinate 0-05%
Demulsifier 25 ppm
Defoamer 200 ppm
Pour point depressant 0.2%
Detergent or dispersant 0.3%
Antiwear Additive 0.5%
4. Heat Transfer Oil
Tetrakis-(methylene-3,5 di-tert-butyl-
4-hydroxy-hydrocinnamate) methane 0.1%
Tris-(2,4-di-tert-butylDhenyl) phosphite 0.4%
Rust Inhibitor 0-05%
Detergent or Dispersant 0.1%
35~6
The compositions of the invention are made by normal blending and mixing
techniques, generally at room temperaturP or slightly elevated temperature to
aid in dissolution of the ingredients. Any of the generally-used types of
blending apparatus can be employed, including fixed in-line blenders and batch
5 stirrers.
Example 1
Several lubricating oil compositions exemplifying the invention
were made by simple mixing of a hindered phenol, namely tetrakis-(methylene-
10 3,5-di-tert-butyl-4-hydroxy-hydrocinnarnate) methane, a phosphite, namely
tris-(2,4-di-tert-butyl-phenyl) phosphite, and hydrotreated lubricating oil of
ISO 32 grade manufactured by Gulf Canada, in the proportions shown in Table
Z. The results of an extended IP-48 oxidation stability test on each mixture
are shown also in the table, and illustrate the synergistic action of the
15 antioxidant rnixture.
Example 2
The two antioxidants of Example 1 were mixed in varying
proportions with a second sample of ISO 32 hydrotreated oil, this sample made
20 by Chevron Corporation, in the amounts shown in Table 3. The extended IP-48
oxidation stability test results confirm the synergistic action of the mixture of
antioxidants in this type of hydrotreated oil.
Example 3
-
The same antioxidants as in Examples 1 and 2 were mixed with a
poly-alpha-olefin synthetic oil, and tested as in Examples 1 and Z. The
synergism with the poly-alpha-olefin oil was confirmed.
- 10 -
12'~8~16
o ~
O ~ _1 J
O O 0
~ o U`~
OD O
o o V~
O O ~ ~ _l
~;1 ` ~ o
o
O O ~ ~D J
_, ae c~
~ ~ ~ o o~ J~ o
$ aO~ o Ir~ _l
o o ~ ~i o
C~ t~ ~ o~ 1-- 0
O O Cr~ ~ o
o ~ ~ ~ r~
- C
~ E _ c Q
i ~ ~' ' ¦ = E
~ ~5~>~C ~ ~ L j ¦ ~ ~
. . .
1~248516
o o~
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o c~
3e 0
~; o o o~
E
o o ` C~ o
", o o o~ ~ o
_~ O ~ ~ r~
o o
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E
- 12 -
~85~6
o
o o U~ o o
~e O
o~ o o~
o o ~ ~ U~
ae O
~ ~ o~ ~ o
~ o o o~
Z ae O
o~ "~, o,
E
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.el ~ ~ o
~Do ~ o~ I~
O o o~
c
v a~
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~1
:'
lZ~8~i:16
,_ o o ~ C~,
o o o~
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o o ~ ~ ~
u~ ~ ~ ~ ~D O
E o o ~ co o
~ o o ~CO o
F
8 ~ o ~ ~
- o o o~ CO o
o U~
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`: - 14 -
1~48516
~ ~0 ` ~
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z
o o o~
o~
E
$
- o o o ~ I` ~
w
x
V _~
CL ~ _ ¦ ~
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- 15 -
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ae O
O U' ~ o,
o o ~ _ U`\
~e O
o o ~ ~ ~
ae O
o
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E
,~ o ~o
o
o o
.~
o u~ O~ o
V
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o
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,~ u =. c r
~ x ~ ~ _ ~ E
c o L. " ~ O~
- 16 -
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Exam~e 4
Several lubricating oil compositions were made in the same manner
as Example 1 using the same oil and phenol stabilizer, and usin~ bis-(2,4-di-
tert-butyl phenyl) pentaerythritol disphosphite as the phosphite stabilizer. Theoxidation stability results confirm the synergism of the second type of
phosphite in compositions accorcling to the invention.
Example 5
The phosphite stabilizer and lubricatiny oil of Example 1 were
mixed with a different hindered phenol, thio diethylene bis-(3,5-di-tert-butyl-
4-hydroxy-hydrocinnamate) in varying proportions and with a rust inhibitor in
the amount of 0.5 per cent. This phenol is also shown to exhibit synergism
with the phosphite, by the oxidation stability results in Table 6.
By way of contrast to the specific oils included in the invention,
the antioxidants of Example 1 were used in compositions in which the oil was a
solvent-refined oil. The mixtures of antioxidant produced no significant
improvement in the oxidation stability, as illustrated in Table 7. The solvent-
refined oil contained 14.4 per cent aromatics, 0.2 per cent thiophenes and 1.3
per cent polar compounds including 500 ppm of sulphur and 25 ppm of nitrogen.
It will be seen that lubricant compositions according to the
invention are advantageous for use in applications where the lubricant is
exposed to an oxidizing environment and high temperatures, for example
compressor oils, heat transfer oils, hydraulic fluids and steam turbine oils.
- 17 -
